Positioning actuators are used inter alia in motor vehicles in the area of automatically actuated separator clutches and, within the drive-train concerned, bring about the opening or closing of the separator clutch. For this, positioning actuators are usually in the form of actuating pistons which, to produce the required adjustment movements, are supplied as necessary with a working medium, the working medium often being compressed air in the commercial vehicle sector. The inflow of the working medium is usually controlled by one or even more than one valve. In particular, however, in the case of a separator clutch in the form of a friction clutch, from the standpoint of operating time a contact point can be displaced as a result of wear and this entails adapting operating parameters of the positioning actuator for control purposes in order to ensure, as before, that during driving operation the separator clutch is opened and closed in a reliable and comfort-orientated manner. Accordingly sensors are often provided in the area of the positioning actuator concerned, by way of which an operating force of the actuator can be deduced in each case and by taking into account at the same time a current clutch position, a wear-related displacement of a characteristic curve of the separator clutch can be recognized. Sometimes, however, an operating force of a positioning actuator is also determined by computation, in order to be able to determine it even without the use of sensors and therefore in a more cost-effective manner.
In DE 10 2007 022 126 A1 a method for determining a characteristic parameter of a positioning actuator is described, which actuator is in the form of a piston-cylinder unit. The characteristic parameter to be determined is, among others, an operating force of the positioning actuator, and for that purpose a computation module is used and a determination is carried out with the help of a simulation.